With the increase in electronic commerce, the encryption of proprietary information and the application of electronic signatures to documents and other content is becoming more widespread. In some cryptography based systems, such as those employing public key cryptography techniques, digital signature key pairs (a private key and a public key) are used to authenticate a digital signature of a subscriber to ensure that a message sent by a subscriber actually came from the subscriber sending the message. In addition to digital signature key pairs, encryption key pairs are also generally used to encrypt the data being sent from one subscriber to another subscriber.
Certificates are generated by a manager or trusted certification authority, such as a network server, for the public keys of the private/public key pair to certify that the keys are authentic and valid. The public keys and certificates are used for two main purposes: verifying a digital signature and encrypting information. The receiver of a digitally signed e-mail or document for example, typically uses the public key in the sender's certificate to verify the digital signature of the sender. A subscriber wishing to send encrypted e-mail first encrypts the e-mail with a random symmetric key, then uses the intended receiver's public key to encrypt the symmetric key and then attaches the encrypted symmetric key to the encrypted e-mail so that the receiver can decrypt the e-mail. A subscriber unit sending a message sends the encrypted data with its digital signature along with a certificate.
The certificate has the certification authority's signature embedded as part of the certificate. A receiver validates the digital signature by looking at the received certificate. Each client stores a certification authority public key to verify that the certificate was made by the trusted certification authority.
In typical public key cryptography systems, the certification authorities are capable of revoking public key certificates if for example the user's privileges are withdrawn. The certification authority also revokes certificates if the public key of a subscriber is somehow compromised and the subscriber or security personnel notifies a certification authority that the certificate should be revoked so that subsequent receivers of the public key certificate are not fooled into thinking that the sender is the actual subscriber sending the message. For example, in the case of a stolen private key, the unscrupulous holder of the stolen private key could act as the proper user. However if the certification authority revokes the public key certificate for that subscriber, all subscribers receiving messages from the subscriber using a revoked public key certificate are notified through a certificate revocation list (CRL) listing the revoked certificates. Therefore a receiver of a message from an unscrupulous hacker can determine that the content of the message is untrustworthy. In prior art public key cryptography systems, in addition to CRLs, authority revocation lists (ARL) are also typically generated by certification authorities. The authority revocation lists indicate that a particular certification authority has been revoked so that all certificates issued from that certification authority are no longer valid.
As more and more electronic transactions are being made via electronic based networks, digital signature data and other digital data may need to be authenticated at a later date, for example in legal proceedings many years after an electronic agreement was executed. For example, if a wire transfer had been made electronically from one client to another and a dispute arises fifty years later, a mechanism is needed to ensure that the digital signature on the wire transfer was in fact authentic at the time it was sent and that the transaction was wired by authorized personnel. In addition, as technology becomes more efficient at breaking cryptographic codes, digital documents that are digitally signed at one point in time may be easy to forge ten years later which may allow an unscrupulous person to attempt to modify the terms of a contract or wire transfer. As such, the proper archival of digital data can be essential to ensuring that long term confidence in electronic transactions and communication of other information is maintained. Later evaluation and scrutiny of electronic commercial transactions, electronic contracts and other data may be necessary to avoid repudiation by parties involved. A problem arises if important information is not archived in a timely and proper manner since the information may be lost or may be exposed to tampering by an unscrupulous party. Also, archival can require the use of large and expensive storage capacity.
Accordingly, with electronic commerce dispute resolution requirements it can be difficult to reconstruct electronic transactions many years later. A typical transaction may include, for example, digital signatures and corresponding public key certificates, in the case where public key infrastructure is used. As such, such certificates may expire over a period of time and need to have their authenticity restored. Non-repudiation services are described, for example, in ISO-13888. In addition, validation authorities are known which may have a first party sender certificate for validation to a trusted third party authority. The trusted third party authority then finds a certificate's revocation status information, such as associated CRLs and returns a yes or no answer to the requesting party indicating whether the certificate is valid. Other systems may provide some type of restoration of authenticity, such as where a trusted authority uses a notary service where the notary service may apply a time stamp and associated digital signature to information sent to it. The notary may verify the digital signature of one or more certificates to confirm that they were authentic, at least at the time that the notary received the information. However, such systems do not generally provide archival of electronic transaction evidence information or retrieval of that information. Although archival services are known that periodically time stamp the information, such information is not typically archived in an efficient manner to reduce storage requirements since such known offsite archival systems may only store the exact transaction information without determining whether or not any redundant information may be present.
Consequently, a need exists for an apparatus and method for electronic transaction evidence archival and retrieval that facilitates a reduction in storage requirements while also providing a restoration of authenticity of stored information, if desired.